Boot System Priority Control - HP 340 Series Service Manual

Boot System Priority Control
Devices are searched in priority order for systems. This priority order is determined by the boot
list shown below:
1. Disc drives at select codes
o-:n
on bus address 0, unit 0, volume 0
2. Remaining disc drives at select codes 0-31, bus addresses 0-7, units 0-16, volurnes 0-7
Each device is allowed to have multiple systems. Again, if the SPU is unattended, it will boot
the first system found. If the SPU is attended (i.e. a key was struck after the input human
interface was initialized), it will display all systems found until a system is selected and that
system is found.
For each category in the boot list, there is also an order of search based on address location.
In all cases, lower addresses are found first. This means a device at select code 0 will be found
before a device at select code 7. If a device has multiple addresses to locate it, then searching
is done at a local level first. For example, after looking at select code 7, bus address 1, unit 1,
the Boot ROM will look at select code 7, bus address 1, unit 2 before going to select code 8.
The boot list was designed to make it easy to change and control which systeln will be booted
in the unattended mode. The guidelines used to establish the boot list are as follows:
• High priority addresses before low priority addresses.
• Local systenls before remote systems (Local refers to dedicated devices and remote refers
to shared devices.).
• Removable media before non-removable media.
• Small capacity devices before large capacity devices.
Default Mass Storage Is
The Boot ROM is responsible for setting up the default mass storage variable,
DEFAULT _MSUS. It is used by systems for three purposes as the:
• Default MS US for operating systems.
• Device from which to load an autostart program, and
• Device from which to do a secondary load.
The DEFAULT _MSUS is set to the following algorithm which is the:
• SaIne as the MSUS of the booted system, OR a A non-ROM value passed in
DEFAULT _MSUS to the booter routine (this is done only by systems calling the booter,
not by the Boot ROM itself), or
• First device found present in the boot list if ROM is specified in DEFAULT _MSUS and
no media can be found (i.e., an on-line disc drive with no media present).
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Boot ROM Functions